In 1997 Mr Wilf Righter designed ZX97 - a ZX81
equivalent computer without dedicated ULA chip, with all logic made
using 74HC-series chips. ZX97 contained additional RAM disk and parallel
port. It was quite large, as it was assembled on 3 Euro-card format
modules.
In 1998 a lite version has been designed, which could be fit on a
single-sided PCB (yet with lots of wires). This "lite" version has no
parallel port or RAM disk, but still has tape I/O.
This is my unit, built from original ZX97Lite PCB, using 74HC logic.

-
HERE is a PCB tracks drawing (with one mistake).
Schematic has one more diffeence - Pin 4 of U10 is connected directly to
/RFSH on PCB. If image doesn't download - change slash to proper.
- HERE
is a schematic, parts list and keyboard description. There's also a ROM
dump.
- Here's a
copy of it.
- Here's a
Croatian page of someone who also built a ZX97Lite. More of his photos:
here

This placement sheet will
help you to figure out what goes where. Remember to double-check for
shorted tracks. During assembling IC sockets may require machining to
fit over wires.

There are following errors on PCB:
- RAM /WR Line (pin 27) should have pull-up resistor
- U14 pin 14 should be connected to Vcc, NOT GND!Here is another version of PCB which has
fixed the last error.

Here are keyboard stickers for
ZX97Lite. I've used keys from old programmable keyboard so I could
remove small piece of transparent plastic and insert them under it.

Keyboard layout (from EightyOne emulator):

The difference between this and ZX81 are 3 keys with
commands DIRECTORY (DIR), HLOAD and HSAVE.
- DIRECTORY displays RAM disk directory. Because there's no RAM disk in
ZX97Lite, rOM disk with assembler/disassembler is displayed.
- HLOAD loads program from parallel port
- HSAVE outputs current program to parallel port. Because ZX97Lite has no
parallel port, these 2 commands just hang ZX97lite.

One more thing: While testing my unit, I've found some
problems with U20 and U21. The symptom is when inverted-video character
is displayed and some lines of it blink. I've fixed this problem by
adding 100n decoupling capacitor to U21.